The present invention relates to an antenna shaft positioning device, and more particularly, to an apparatus used to stop a rotating shaft at a precise angular position between two end stops.
It is known in the art to use mechanical limit stops to position a shaft. U.S. Pat. No. 2,844,038 to Danta discloses a bi-directional mechanical stop system which provides for two opposed limit stops. An additional rotation-limiting apparatus is disclosed in U.S. Pat. No. 2,487,349 to Marholz which describes an apparatus for limiting the rotation of a driven shaft to a predetermined number of revolutions from a reference point. These and other like prior art devices provide for stopping rotation of a mechanism between two fixed points, however, they fail to teach means for precisely stopping the motion of a rotating shaft at a distinct point in the shaft's axis of rotation in between two fixed end stops in a manner suitable for use with a highly accurate attenna movement. An antenna shaft must be stopped at a precise location without exceptional jarring that might damage a delicate antenna mast. Thus, while halting the rotation of an element at two points is typically achieved through the use of two end stops, periodically stopping a rotating shaft precisely at a fixed intermediate point, in between the two end stops, requires a mechanism which can capture the rotating element at the intermediate point when desired, and yet at other times allow the shaft to rotate bidirectionally between the two end stops.
It is an object of the present invention, therefore, to provide a shaft arresting means suitable for selective stopping an antenna shaft at an intermediate point in its rotation without damaging that antenna.
It is a further object of the invention to provide a fail-safe locking mechanism which stops the antenna at a preferred intermediate position of power is lost.